The invention relates to a novel process for preparing 2-halo-6-aminopurine compounds and derivatives thereof, comprising halogenation of 2,6-diaminopurine compounds at the C-2 position to give the corresponding halogenated compounds, including halogenated 
nucleosides. These nucleosides, e.g., 2-chloro-6-aminopurine-2xe2x80x2-deoxyribonucleoside, i.e., the compound with the above structure wherein R is 2xe2x80x2-deoxyribose and X is Cl (2-chloro-2xe2x80x2-deoxyadenosine), are useful as antileukemic agents, e.g., in treating leukemias such as hairy cell leukemia.
The invention also relates to methods for the synthesis of acyclic derivatives of 2-halo-6-aminopurines and 2-halo-6-aminopurine morpholino derivatives which are useful in the preparation of synthetic oligonucleotide analogs.
Processes for preparing 2-chloro-6-aminopurine-2xe2x80x2-deoxyribonucleoside (2-chloro-2xe2x80x2-deoxyadenosine, hereinafter xe2x80x9c2-CdAxe2x80x9d) and other 2-chloro-6-aminopurines are known in the art. Such processes are described in, e.g., U.S. Pat. No. 4,760,137; Kazimierzuk et al., J. Am. Chem. Soc., 106:6379, 1984; Wright et al., J. Org. Chem., 52:4617, 1987 and Christensen et al., J. Med. Chem., 15:735, 1972. The preparation of 2-CdA described by these workers requires the glycosylation of a dihalogenated purine to give an intermediate dihalogenated nucleoside which is then transformed into the desired nucleoside. More specifically, these workers described the glycosylation of 2,6-dichloropurine with 1-chloro-2xe2x80x2-deoxy-3xe2x80x2,5xe2x80x2-di-O-p-toluyl-xcex2-D-erythropentofuranose to give a mixture of N-7 and N-9 isomers of 2,6-dichloro-(2xe2x80x2-deoxy-3xe2x80x2,5xe2x80x2-di-O-p-toluyl-xcex2-D-erythropentofuranosyl)-purine. This process suffers from several shortcomings, such as the formation of isomeric side products at the 1xe2x80x2-carbon and the utilization of costly starting materials, such as 2,6-dichloropurine.
U.S. Pat. No. 5,208,327 discloses a method for preparation of 2-CdA from guanosine in eight steps via a 2-chloroadenosine intermediate in 2.8% overall yield (from guanosine). This method is inefficient and requires several protection and deprotection steps in order to remove the 2xe2x80x2 hydroxyl to yield a 2xe2x80x2-deoxy product. The synthesis of the 2-chloroadenosine intermediate also disclosed in the same patent uses protecting group chemistry and an alternate halogenation/amination strategy. This process is extremely expensive because of the multiple steps involved and the use of expensive 2-chloroguanosine starting material, and is not suitable for truly large scale production.
Processes for the preparation of compounds of the formula: 
wherein R1 is acyl or tolyl and W1 and W2 are independently halogen or amino from the corresponding per-O-protected nucleosides are disclosed, e.g., in Robins and Uznanski, Can. J. Chem. 59, 2601, 1981; Montgomery and Hewson, J. Med. Chem. 12, 498, 1969; and Huang et. al. J. Med. Chem., 27, 800-802, 1984. The transformation of the starting nucleosides to 2-halopurines requires several steps, including diazotization of the 2-amino intermediates in non-polar organic solvents, followed by halogenation. Thus, this method is completely unfeasible when it is necessary to utilize starting materials that are not soluble or only sparingly soluble in non-polar organic solvents, in contrast to the methods of the present invention, detailed below.
Methods for the conversion of unprotected purine ribonucleosides having the formula: 
wherein R1 is hydrogen, W3 is halogen or hydrogen, and W1 and W2 are independently amino or halogen, to 2-halogenated nucleosides are known in the art (Gerster et. al., J. Org. Chem., 33, 1070, 1968; Gerster et. al., J. Org. Chem., 31, 3258, 1966; Gerster et. al., J. Am. Chem. Soc, 87, 3752, 1965). However, these methods provide low yields of products, and require reactions to be performed with sodium nitrite at temperatures below 0xc2x0 C. in aqueous solution, thus making drying and separation of products difficult. The prior art also discloses that diazotization of 2-amino groups is only possible for ribonucleosides, because the reaction conditions cleave the glycosyl linkage of the corresponding deoxynucleosides (see Montgomery and Hewson, J. Med. Chem. 12, 498, 1969).
Thus, while the prior art discloses processes for the preparation of 2-CdA and other 2-halo-6-amino nucleosides and deoxynucleosides, these methods all have disadvantages, such as including a glycosylation reaction, or the need for a series of nucleoside hydroxyl protection/deprotection reactions, or the need to manipulate 2-halo-ribonucleosides or analogs at sub-zero temperatures using aqueous reaction conditions.
The present inventors have now surprisingly and unexpectedly discovered methods that make it possible to convert unprotected 2xe2x80x2- or 3xe2x80x2-deoxynucleosides, ribonucleosides or analogs to the corresponding 2-halo derivatives. Also discovered by the present inventors are methods for performing such transformations on unprotected nucleosides where the unprotected nucleosides are highly insoluble in non-polar organic solvents.
The present invention overcomes the difficulties and shortcomings of the prior art with regard to the synthesis 2-halo-6-aminopurine compounds and derivatives thereof and especially of 2-halogenated purine ribonucleosides and 2-halogenated-2xe2x80x2- and 3xe2x80x2-deoxy and 2xe2x80x2 and 3xe2x80x2-substituted purine ribonucleosides. Disclosed herein are methods for producing 2-halo-6-aminopurine compounds and derivatives thereof and especially 2-halogenated-2xe2x80x2-deoxy purine nucleosides, 2-halogenated purine ribonucleosides, and 2xe2x80x2 and 3xe2x80x2-substituted analogs thereof via halogenation at the 2 position in a unique organic solvent system at room temperature.
Thus, in one aspect the invention relates to methods for producing 2-halo-6-amino derivatives, comprising the steps of:
admixing a nonpolar aprotic organic solvent with a polar aprotic organic solvent to produce a solvent mixture;
dissolving in the solvent mixture a compound having the formula 
where R is selected from the group consisting of hydrogen, C1 to C20 alkyl, including linear and branched chain alkyl, cycloalkyl, alkoxyalkyl, alkylamino, ether, thioether, haloalkyl, a monocyclic aryl group, a multicyclic aryl group, a heterocyclic aryl group having from 1 to 20 carbon atoms and 1 to 10 heteroatoms, sugar moieties selected from the group consisting of xcex2-D-ribofuranosyl, deoxy-xcex2-D-furanosyl, xylofuranosyl, arabinofuranosyl, and 2xe2x80x2-, 3xe2x80x2-, and 2xe2x80x2,3xe2x80x2-substituted or derivatized analogs of xcex2-D-ribofuranosyl, deoxy-xcex2-D-furanosyl, xylofaranosyl, and arabinofuranosyl sugar moieties; and
reacting the compound in the solvent mixture with an organic nitrite and a metal halide, where the metal halide is a Lewis acid, to produce a reaction product.
In another aspect the invention relates to the methods for producing 2-halonucleosides comprising the steps of:
admixing a nonpolar aprotic organic solvent with a polar aprotic organic solvent to produce a solvent mixture;
dissolving in the solvent mixture a nucleoside having the formula 
xe2x80x83where Q is O or S;
where R1 and R2 together form a moiety with the formula Oxe2x80x94A(Y)xe2x80x94O, where A is C, S, or Pxe2x80x94R and where Y is O, S, Nxe2x80x94R, or 2R;
or where R1 and R2 are independently hydrogen, Oxe2x80x94R, R, Nxe2x80x94R2, N3, X, or Sxe2x80x94R;
where R is hydrogen, C1 to C20 alkyl, including linear and branched chain alkyl, cycloalkyl, alkoxyalkyl, alkylamino, ether, thioether, haloalkyl, a monocyclic aryl group, a multicyclic aryl group, or a heterocyclic aryl group having from 1 to 20 carbon atoms and 1 to 10 heteroatoms and where X is Cl, Br, F, or I; and
reacting the nucleoside in the solvent mixture with an organic nitrite and a metal halide, where the metal halide is a Lewis acid, to produce a reaction product.
In yet another aspect the invention relates to the methods for producing 2-halo-6-aminoalkyloxy derivatives comprising the steps of:
admixing a nonpolar aprotic organic solvent with a polar aprotic organic solvent to produce a solvent mixture;
dissolving in the solvent mixture a nucleoside analog having the formula 
xe2x80x83where R1 is hydrogen, CH2OH, or CH2OPOM; R2 is OH, OPh, or OPOM; and R3is OH, OPh, or OPOM;
or where R1 and R2 form the moiety xe2x80x94CH2Oxe2x80x94 and R3 is OH, wherein POM is pivalyloxymethyl; and
reacting the nucleoside analog in the solvent mixture with an organic nitrite and a metal halide, where the metal halide is a Lewis acid, to produce a reaction product.
In one particular aspect, the invention relates to methods for producing 2-halo-6-aminopurine-2xe2x80x2-deoxy or 2xe2x80x2-substituted nucleosides comprising the steps of:
admixing a nonpolar aprotic organic solvent with a polar aprotic organic solvent to produce a solvent mixture;
dissolving in the solvent mixture an unprotected nucleoside having the formula 
xe2x80x83where R1 is hydrogen, OR, R, NR2, N3, X, or SR; R is hydrogen, C1 to C20 alkyl, including linear and branched chain alkyl, cycloalkyl, alkoxyalkyl, alkylamino, ether, thioether, haloalkyl, a monocyclic aryl group, a multicyclic aryl group, or a heterocyclic aryl group having from 1 to 20 carbon atoms and 1 to 10 heteroatoms, and X is Cl, Br, F, or I; and
reacting the unprotected nucleoside in the solvent mixture with an organic nitrite and a metal halide, where the metal halide is a Lewis acid, to produce a reaction product.
In another aspect, the invention relates to methods for producing 2-halo-6-aminopurine-3xe2x80x2-deoxy or 3xe2x80x2-substituted nucleosides comprising the steps of: admixing a nonpolar aprotic organic solvent with a polar aprotic organic solvent to produce a solvent mixture;
dissolving in the solvent mixture an unprotected nucleoside having the formula 
xe2x80x83where R1 is hydrogen, OR, R, NR2, N3, X, or SR; R is hydrogen, C1 to C20 alkyl, including linear and branched chain alkyl, cycloalkyl, alkoxyalkyl, alkylamino, ether, thioether, haloalkyl, a monocyclic aryl group, a multicyclic aryl group, or a heterocyclic aryl group having from 1 to 20 carbon atoms and 1 to 10 heteroatoms, and X is Cl, Br, F, or I; and
reacting the unprotected nucleoside in the solvent mixture with an organic nitrite and a metal halide, wherein the metal halide is a Lewis acid, to produce a 2-halo-6-aminopurine reaction product.
In a further aspect, the present method comprises a method for stabilizing the 2-haloadenosine and 2-halo-deoxyadenosine reaction products produced by the synthetic methods of the present invention comprising subjecting the reaction products to resin column chromatography.
In another aspect, the invention relates to methods for producing 2-halo-6-aminopurine-2xe2x80x2,3xe2x80x2-dideoxy nucleosides comprising the steps of: admixing a nonpolar aprotic organic solvent with a polar aprotic organic solvent to produce a solvent mixture;
dissolving in the solvent mixture an unprotected nucleoside having the formula 
xe2x80x83where Q is O or S; and
reacting the unprotected nucleoside in the solvent mixture with an organic nitrite and a metal halide, wherein the metal halide is a Lewis acid, to produce a 2-halo-6-aminopurine reaction product.
Another aspect the invention relates to the methods for producing 2-halo-6-aminopurine-4-thionucleosides comprising the steps of:
admixing a nonpolar aprotic organic solvent with a polar aprotic organic solvent to produce a solvent mixture;
dissolving in the solvent mixture a 4-thionucleoside having the formula 
xe2x80x83where R1 and R2 are independently hydrogen, OR, R, NR2, N3, X, or SR;
where R is linear or branched chain alkyl, cycloalkyl, alkoxyalkyl, ether, thioether, haloalkyl, a monocyclic aryl group, a multicyclic aryl group, or a heterocyclic aryl group having from 1 to 20 carbon atoms and 1 to 10 heteroatoms, and X is Cl, Br, F, or I; and
reacting the nucleoside in the solvent mixture with an organic nitrite and a metal halide, where the metal halide is a Lewis acid, to produce a reaction product.
Yet another aspect the invention relates to the methods for producing 2-halo-6-aminopurine-2xe2x80x2,3xe2x80x2-derivatized nucleosides comprising the steps of:
admixing a nonpolar aprotic organic solvent with a polar aprotic organic solvent to produce a solvent mixture;
dissolving in the solvent mixture a nucleoside having the formula 
xe2x80x83where Q is O or S;
where R1 and R2 together form a moiety with the formula Oxe2x80x94A(Y)xe2x80x94O, where A is C, S, or Pxe2x80x94R and where Y is O, S, Nxe2x80x94R, or 2R;
or where R1 and R2 are independently hydrogen, Oxe2x80x94R, R, Nxe2x80x94R2, N3, X, or Sxe2x80x94R; where R is linear or branched chain alkyl cycloalkyl, alkoxyalkyl, ether, thioether, haloalkyl, a monocyclic aryl group, a multicyclic aryl group, or a heterocyclic aryl group having from 1 to 20 carbon atoms and 1 to 10 heteroatoms, and X is Cl, Br, F, or I;
reacting the nucleoside in the solvent mixture with an organic nitrite and a metal halide, where the metal halide is a Lewis acid, to produce a reaction product.
In one particular aspect, the invention relates to methods for producing 2-halo-6-aminopurine-2xe2x80x2-deoxy or 2xe2x80x2-substituted N-7 glycosylated nucleosides comprising the steps of:
admixing a nonpolar aprotic organic solvent with a polar aprotic organic solvent to produce a solvent mixture;
dissolving in the solvent mixture an unprotected N-7 glycosylated nucleoside having the formula 
xe2x80x83where Q is O or S;
where R1 and R2 together form a moiety with the formula Oxe2x80x94A(Y)xe2x80x94O, where A is C, S, or Pxe2x80x94R and where Y is O, S, Nxe2x80x94R, or 2R;
or where R1 and R2 are independently hydrogen, Oxe2x80x94R, R, Nxe2x80x94R2, N3, X, or Sxe2x80x94R;
where R is linear or branched chain alkyl, cycloalkyl, alkoxyalkyl, ether, thioether, haloalkyl, a monocyclic aryl group, a multicyclic aryl group, or a heterocyclic aryl group having from 1 to 20 carbon atoms and 1 to 10 heteroatoms, and X is Cl, Br, F, or I; and
reacting the unprotected nucleoside in the solvent mixture with an organic nitrite and a metal halide, where the metal halide is a Lewis acid, to produce a reaction product.
In yet another aspect, the present invention is directed to novel morpholino 2-halopurines of the formula: 
where X is fluorine, chlorine, bromine, or iodine and R1 is alkyl, aryl, substituted aryl, aryloxy, or substituted aryloxy, and methods for synthesizing such compounds.
All patents, patent applications, and literature references cited herein are incorporated by reference in their entirety. In case of a conflict in terminology, the present specification controls.
The following terms generally have the following meanings.
The term xe2x80x9carylxe2x80x9d refers to aromatic groups, which have at least one ring having a conjugated pi electron system, including for example carbocyclic aryl, heterocyclic aryl and biaryl groups, all of which may be optionally substituted. Carbocyclic aryl groups are groups wherein all the ring atoms on the aromatic ring are carbon atoms, such as phenyl. Also included are optionally substituted phenyl groups, being preferably phenyl or phenyl substituted by one to three substituents. Further included are phenyl rings fused with a five or six membered heterocyclic aryl or carbocyclic ring, optionally containing one or more heteroatoms such as oxygen, sulfur, or nitrogen. Where chemical groups or moieties are indicated to be xe2x80x9coptionally substitutedxe2x80x9d, it is meant that the groups can be chemically bonded to one or more other chemical groups, such groups preferably being, but not limited to, lower alkyl, hydroxy, lower alkoxy, lower alkanoyloxy, halogen, cyano, perhalo lower alkyl, lower acylamino, lower alkoxycarbonyl, amino, alkylamino, carboxamido, and sulfamido.
Heterocyclic aryl groups are monocyclic or polycyclic groups having from 1 to 10 heteroatoms as ring atoms in the aromatic rings and the remainder of the ring atoms carbon atoms. Suitable heteroatoms include oxygen, sulfur, and nitrogen. Heterocyclic aryl groups include furanyl, thienyl, pyridyl, pyrrolyl, pyrimidyl, pyrazinyl, imidazolyl, and the like, all optionally substituted.
Optionally substituted furanyl represents 2- or 3-furanyl or 2- or 3-furanyl preferably substituted by lower alkyl or halogen. Optionally substituted pyridyl represents 2-, 3- or 4-pyridyl or 2-, 3- or 4-pyridyl preferably substituted by lower alkyl or halogen. Optionally substituted thienyl represents 2- or 3-thienyl, or 2- or 3-thienyl preferably substituted by lower alkyl or halogen.
The term xe2x80x9caralkylxe2x80x9d refers to an alkyl group substituted with an aryl group. Suitable aralkyl groups include benzyl, picolyl, and the like, and may be optionally substituted.
The term xe2x80x9clowerxe2x80x9d referred to herein in connection with organic radicals or compounds respectively defines such with up to and including 7, preferably up to and including 4 and advantageously one or two carbon atoms. Such groups may be straight chain or branched.
The terms (a) xe2x80x9calkylaminoxe2x80x9d, (b) xe2x80x9carylaminoxe2x80x9d, and (c) xe2x80x9caralkylaminoxe2x80x9d, respectively, refer to the groups xe2x80x94NRRxe2x80x2 wherein respectively, (a) R is alkyl and Rxe2x80x2 is hydrogen, aryl or alkyl; (b) R is aryl and Rxe2x80x2 is hydrogen or aryl, and (c) R is aralkyl and Rxe2x80x2 is hydrogen or aralkyl.
The term xe2x80x9cacylaminoxe2x80x9d refers to RC(O)NRxe2x80x2.
The term xe2x80x9ccarbonylxe2x80x9d refers to xe2x80x94C(O)xe2x80x94.
The term xe2x80x9cacylxe2x80x9d refers to RC(O)xe2x80x94 where R is alkyl, aryl, aralkyl, or alkenyl.
The term xe2x80x9ccarboxamidexe2x80x9d or xe2x80x9ccarboxamidoxe2x80x9d refers to xe2x80x94CONRR wherein each R is independently hydrogen, lower alkyl or lower aryl.
The term xe2x80x9calkylxe2x80x9d refers to saturated aliphatic groups including straight-chain, branched chain and cyclic groups, optionally containing one or more heteroatoms.
The invention in one aspect relates to a novel process for preparing the compound 2-CdA and other 2-halogenated purine nucleosides and 2-halogenated 2xe2x80x2-deoxy and 2xe2x80x2 substituted nucleosides having the formula: 
where R1 is hydrogen, OR, R, NR2, N3, X, or SR; R is hydrogen, C1 to C20 alkyl, including linear and branched chain alkyl and cycloalkyl, alkoxyalkyl, alkylamino, ether, thioether, haloalkyl, a monocyclic aryl group, a multicyclic aryl group, or a heterocyclic aryl group having from 1 to 20 carbon atoms and 1 to 10 heteroatoms, and X is Cl, Br, F, or I.
The method comprises admixing a nonpolar aprotic organic solvent with a polar aprotic organic solvent to produce a solvent mixture, dissolving or suspending in the solvent mixture an unprotected nucleoside having the formula: 
where R1 is hydrogen, OR, R, NR2, N3, X, or SR; R is hydrogen, C1 to C20 alkyl, including linear and branched chain alkyl, cycloalkyl, alkoxyalkyl, alkylamino, ether, thioether, haloalkyl, a monocyclic aryl group, a multicyclic aryl group, or a heterocyclic aryl group having from 1 to 20 carbon atoms and 1 to 10 heteroatoms, and X is Cl, Br, F, or I; and reacting the unprotected nucleoside in the solvent mixture with an organic nitrite and a metal halide, where the metal halide is a Lewis acid, to produce a reaction product.
Methods for the synthesis of the 2xe2x80x2-deoxy, 2xe2x80x2-OH, and 2xe2x80x2-O-alkyl nucleoside diaminopurine starting materials are known in the art. Syntheses of many exemplary starting materials are described in such works as: Chemistry of Nucleosides and Nucleotides, Vol. 1, Ed. Townsend, L. B., Plenum Press, New York, N.Y., 1988; Chemistry of Nucleosides and Nucleotides, Vol 2., Ed. Townsend, L. B., Plenum Press, New York, N.Y., 1991; Chemistry of Nucleosides and Nucleotides, Vol. 3, Ed. Townsend, L. B., Plenum Press, New York, N.Y., 1994; Oligonucleotide Synthesis: A Practical Approach, Ed. Gait, M. J., Oxford Univ. Press, New York, N.Y., 1984; Oligonucleotides and Analogues: A Practical Approach, Ed. Eckstein, F., Oxford Univ. Press, New York, N.Y., 1991. Syntheses of such starting materials are also described, e.g., in U.S. Pat. Nos. 5,506,351 and 5,571,902.
Methods for the synthesis of 2xe2x80x2-fluoro and other 2xe2x80x2-haloribonucleosides (i.e., where R1 is halogen) are described in, e.g., U.S. Pat. No. 5,420,115, European Patent application 417999; Tuttle, J. V.; Tisdale, S. M. and Krenitsky, T. A., J. Med. Chem., 36(1): 119-125, 1993; Thomas, H. J.; Tiwari, K. N.; Clayton, S. J.; Secrist, J. A. III and Montgomery, J. A., Nucleosides and Nucleotides, 13 (1-3): 309-323, 1994. Starting materials for the synthesis of compounds of the invention where R1 is N3 can be obtained by substitution of 2xe2x80x2-halo nucleosides. Starting materials for the synthesis of compounds of the invention where R1 is NHxe2x80x94R can be obtained by reduction of these N3 compounds.
In a preferred embodiment, X is bromine, chlorine, fluorine, or iodine, and R1 is hydrogen.
In other preferred embodiments, X is bromine, chlorine, fluorine, or iodine, and R1 is hydroxyl or is OR, where R is hydrogen, C1 to C20 alkyl, including linear and branched chain alkyl, cycloalkyl, alkoxyalkyl, alkylamino, ether, thioether, haloalkyl, a monocyclic aryl group, a multicyclic aryl group, or a heterocyclic aryl group having from 1 to 20 carbon atoms and 1 to 10 heteroatoms.
In a most preferred embodiment, X is chlorine and R1 is hydrogen.
In another aspect, the invention is directed to methods for synthesizing 2-halogenated purine 3xe2x80x2-O-alkyl, 3xe2x80x2-deoxy, and 3xe2x80x2-substituted ribonucleosides. The methods comprise admixing a nonpolar aprotic organic solvent with a polar aprotic organic solvent to produce a solvent mixture, dissolving or suspending in the solvent mixture an unprotected nucleoside having the formula: 
where R1 is hydrogen, OR, R, NR2, N3, X, or SR; R is hydrogen, C1 to C20 alkyl, including linear and branched chain alkyl, cycloalkyl, alkoxyalkyl, alkylamino, ether, thioether, haloalkyl, a monocyclic aryl group, a multicyclic aryl group, or a heterocyclic aryl group having from 1 to 20 carbon atoms and 1 to 10 heteroatoms, and X is Cl, Br, F, or I; and reacting the unprotected nucleoside in the solvent mixture with an organic nitrite and a metal halide, where the metal halide is a Lewis acid, to produce a reaction product.
Methods for the synthesis of 3xe2x80x2-O-alkyl starting materials are known and widely reported in the art and are described, e.g., in U.S. Pat. No. 5,506,351. The synthesis of unprotected 3xe2x80x2-deoxyribonucleoside is set out in Kumar, A.; Khan, S. I.; Manglani, A.; Khan, Z. K. and Katti, S. B., Nucleosides and Nucleotides 13(5): 1049-1058, 1994. Methods for the synthesis of 3xe2x80x2-substituted nucleosides, e.g., 3xe2x80x2-Fluoro-3xe2x80x2-deoxyribonucleoside are described in Koshida, R.; Cox, S.; Harmenberg, J.; Gilljam, G. and Wahren, B., Antimicrob. Agents Chemother., 33(12): 2083-2088, 1989. Exemplary methods for the synthesis of other 3xe2x80x2-substituted nucleosides, such as 3xe2x80x2-Amino-3xe2x80x2-deoxyribonucleoside are set forth in Kissman, H. M.; Hoffman, A. S.; Weiss, M. J. J. Med. Chem. 6(4): 407-409, 1963; Goldman, L.; Marsico, J. W.; Weiss, M. J. J. Med. Chem. 6(4): 410-412, 1963; Goldman, L.; Marsico, J. W.; J. Med. Chem. 6(4), 413-423, 1963; Soenens, J.; Francois, G.; Van den Eeckhout, E.; Herdewijn, P., Nucleosides and Nucleotides 14(3-5): 409-411, 1995; and Pannecouque, C.; Van Poppel, K.; Balzarini, J.; Claes, P.; De Clercq, E.; Herdewijn, P., Nucleosides and Nucleotides 14(3-5): 541-544, 1995).
Methods for the halogenation of 2,6 diaminonucleosides coupled to sugar moieties such as arabinose and xylose are also within the scope of the present invention. Exemplary syntheses of such starting materials can be found, e.g., in Montgomery, J. A. and Hewson, K., J. Med. Chem., 12: 498-504, 1969; Hansske, F.; Madej, D. and Robins, M. J., Tetrahedron, 40(1): 125-135, 1984 (xylose and arabinose); Krenitsky, T. A., Koszalka, G. W.; Tisdale, J. V.; Rideout, J. L. and Elion, G. B., Carbohydr. Res., 97(1): 139-146, 1981; Krenitsky, T. A., Elion, G. B. and Rideout, J. E., EP 790613; Utagawa, T.; Miyoshi, T.; Morisawa, H.; Yamazaki, A.; Yoshinaga, F. and Mitsugi, K., DE 2835151; Elion, G. B. and Strelitz, R. A., U.S. Pat. No. 4,038,479; Wellcome Foundation, GB 1,386,584; Elion, G. B.; Litster, J. E. and Beachamp, L. M. III, DE 2156637; Elion, G. B. and Strelitz, R. A., DE 205637. Exemplary syntheses of 2xe2x80x2-substituted arabinonucleoside starting materials can be found in, e.g., Robins, M. J.; Zou, R.; Hansske, F. and Wnuk, S. F., Can. J. Chem. 75(6): 762-767, 1997; Watanabe, K. A.; Pankiewicz, K. W.; Krzeminski, J. and Nawrot, B., WO 9211276A1; Tuttle, J. V. and Krenitsky, T. A., EP 285432A2; Watanabe, K. A.; Chu, C. K. and Fox, J. J., EP 219829A2; and Montgomery, J. A.; Shortnacy, A. T.; Carson, D. A. and Secrist, J. A. III, J. Med. Chem., 29(11): 2389-2392, 1986.
Methods for synthesizing 2-halogenated purine 2xe2x80x2,3xe2x80x2-dideoxy nucleosides comprise admixing a nonpolar aprotic organic solvent with a polar aprotic organic solvent to produce a solvent mixture, dissolving or suspending in the solvent mixture an unprotected nucleoside having the formula 
and reacting the unprotected nucleoside in the solvent mixture with an organic nitrite and a metal halide, where the metal halide is a Lewis acid, to produce a reaction product.
Such starting compounds can be prepared according to well-known methods of dideoxy nucleoside syntheses such as those disclosed by Webb II, R. R.; Wos, J. A.; Martin, J. C.; Brodfuehrer, P. R. Nucleosides and Nucleotides, 7(2): 147-153, 1988; Prisbe, E. J.; Martin, J. C. Synth. Comm. 15(5): 401-409 1985; Horwitz, J. P.; Chua, J.; Da Rooge, M. A.; Noel, M.; Klundt, I. L. J. Org. Chem. 31: 205-211, 1966; Horwitz, J. P.; Chua, J.; Noel, M.; Donatti, J. T. J. Org. Chem. 32: 817-818, 1967.
Methods for synthesizing 2-halo 6-aminopurine-4xe2x80x2-thionucleosides comprise admixing a nonpolar aprotic organic solvent with a polar aprotic organic solvent to produce a solvent mixture, dissolving or suspending in the solvent mixture an unprotected nucleoside having the formula 
where R1 and R2 are independently hydrogen, OR, R, NR2, N3, X, or SR; where R is hydrogen, C1 to C20 alkyl, including linear and branched chain alkyl, cycloalkyl, alkoxyalkyl, alkylamino, ether, thioether, haloalkyl, a monocyclic aryl group, a multicyclic aryl group, or a heterocyclic aryl group having from 1 to 20 carbon atoms and 1 to 10 heteroatoms, and X is Cl, Br, F, or I; and reacting the unprotected nucleoside in the solvent mixture with an organic nitrite and a metal halide, where the metal halide is a Lewis acid, to produce a reaction product.
Such starting materials can be prepared according to well-known methods for 4-thionucleosides synthesis, such as those disclosed in Leydier, C.; Bellon, L.; Barascut, J. -L.; Imbach, J. -L. Nucleosides and Nucleotides, 14(3-5): 1027-1030, 1995; Bellon, L.; Leydier, C.; Barascut, J. -L.; Imbach, J. -L. Nucleosides and Nucleotides 12(8): 847-852, 1993, Bellon, L.; Barascut, J. -L.; Imbach, J. -L. Nucleosides and Nucleotides 11(8): 1467-1479, 1992; and Reist, E. J.; Gueffroy, D. E.; Goodman, L. Chem. Ind. (London), 1364, 1964.
Methods for synthesizing 2-halo 6-aminopurine-2xe2x80x2,3xe2x80x2-derivatized ribonucleosides comprise admixing a nonpolar aprotic organic solvent with a polar aprotic organic solvent to produce a solvent mixture, dissolving or suspending in the solvent mixture an unprotected nucleoside having the formula 
where Q is O or S; where R1 and R2 together form a moiety with the formula Oxe2x80x94A(Y)xe2x80x94O, where A is C, S, or Pxe2x80x94R and where Y is O, S, Nxe2x80x94R, or 2R; where R is hydrogen, C1 to C20 alkyl, including linear and branched chain alkyl, cycloalkyl, alkoxyalkyl, alkylamino, ether, thioether, haloalkyl, a monocyclic aryl group, a multicyclic aryl group, or a heterocyclic aryl group having from 1 to 20 carbon atoms and 1 to 10 heteroatoms, and X is Cl, Br, F, or I; and reacting the unprotected nucleoside in the solvent mixture with an organic nitrite and a metal halide, where the metal halide is a Lewis acid, to produce a reaction product.
Starting compounds for such methods, such as isopropylidene nucleosides, can be prepared based upon the methods described in, e.g., Schmidt, O. Th. Methods Carbohydr. Chem., II, 318 (1963); de Belder, A. N. Adv. Carbohydr. Chem. 20: 219, (1965); Hampton, A. J. Amer. Chem. Soc., 83: 3640, 1961; Davis, J. T.; Tirumala, S.; Jenssen, J. R.; Radler, E.; Fabris, D. J. Org. Chem., 60: 4167, 1995; Chladek, S.; Smrt, J. Collect. Czech. Chem. Commun. 28: 1301-1308, 1963; and Anzai, K.; Matsui, M. Bull. Chem. Soc. Jpn. 47: 417-420, 1974. Exemplary syntheses of 2xe2x80x23xe2x80x2thionocarbonate nucleosides are described, e.g., in Anzai, K.; Matsui, M. Agric. Biol. Chem. 37: 345-348, 1973.
Methods for halogenation of 2,6 diaminonucleosides coupled to sugar derivatives at the N-7 position of the base comprise admixing a nonpolar aprotic organic solvent with a polar aprotic organic solvent to produce a solvent mixture, dissolving or suspending in the solvent mixture an unprotected nucleoside having the formula. 
where R1 and R2 are independently hydrogen, OR, R, NR2, N3, X, SR; where Q is O or S; where R is hydrogen, C1 to C20 alkyl, including linear and branched chain alkyl, cycloalkyl, alkoxyalkyl, alkylamino, ether, thioether, haloalkyl, a monocyclic aryl group, a multicyclic aryl group, or a heterocyclic aryl group having from 1 to 20 carbon atoms and 1 to 10 heteroatoms, and X is Cl, Br, F, or I; and reacting the unprotected nucleoside in the solvent mixture with an organic nitrite and a metal halide, where the metal halide is a Lewis acid, to produce a reaction product.
Starting materials having the formula above are known, and can be prepared, e.g., according to the methods set out in Worthington, V. L., Fraser, W., and Schwalbe, C. H.; Carbohydrate Research, 275: 275-284, 1995. N-7 to N-9 or N-9 to N-7 glycosyl transfer reactions are described in the art, e.g., see Seela, F.; Winter, H. Nucleosides and Nucleotides, 14(1and2): 129-142, 1995.
The synthesis of 2-halo-6-aminopurines that have acyclic moieties linked at the N-9 position of the base comprise admixing a nonpolar aprotic organic solvent with a polar aprotic organic solvent to produce a solvent mixture, dissolving or suspending in the solvent mixture an unprotected diaminopurine that has an acyclic moiety linked at the N-9 position of the base, and reacting the unprotected compound in the solvent mixture with an organic nitrite and a metal halide, where the metal halide is a Lewis acid, to produce a reaction product.
Synthesis of diaminopurines that have an acyclic moiety linked at the N-9 position are well-known by those of ordinary skill in the art, and are described, e.g., by Holy, A. and Dvorakova, H., Nucleosides and Nucleotides 14(3-5): 695-702, 1995; Holy, A.; Dvorakova, H and Masojidkova, M., Collect. Czech. Chem. Commun., 60(8): 1390-1409, 1995; Holy, A.; Dvorakova, H.; de Clercq, E.; Desire, A. and Balzarini, J. M. H., WO 9403467; Rosenberg, I. and Holy, A.; Dvorakova, H., Collect. Czech. Chem. Commun., 54(8): 2190-2210, 1989; de Clercq, E.; Holy, A. and Rosenberg, I., Antimicrob. Agents Chemother., 33(2): 185-191, 1989; Yokota, T.; Mochizuki, S.; Konno, K.; Mori, S.; Shigeta, S. and de Clercq, E., Nucleic Acids Symposium Series 22, 17-18, 1990; Holy, A.; Rosenberg, I.; Dvorakova, H. and de Clercq, E., Nucleosides and Nucleotides 7(5-6): 667-670, 1988; Holy, A., Collect. Czech. Chem. Commun., 58(3): 649-674, 1993; Holy, A.; Rosenberg, I. and Dvorakova, H., Collect. Czech. Chem. Commun., 54(9): 2470-2501, 1989; Holy, A. and Rosenberg, I., CS 263955; Holy, A.; Rosenberg, I. and de Clercq, E., EP 253412; and Alexander, P. and Holy, A., Collect. Czech. Chem. Commun., 58(5): 1151-1163, 1993.
Scheme 1, below, sets forth an exemplary process of the present invention, the preparation of 2-CdA. The process utilizes 2,6-diamino purine deoxyriboside (2-amino deoxyadenosine or xe2x80x9cDAPDxe2x80x9d) as a starting material. DAPD can be prepared by methods reported in U.S. Pat. No. 5,506,351 and in Seela and Gabler, Helv. Chim. Acta., 77: 622, 1994. DAPD is also commercially available from Reliable Biopharmaceutical Corporation, St. Louis, Mo. 
DAPD is suspended in a novel solvent combination which includes a polar aprotic organic solvent and a nonpolar aprotic organic solvent, (DMSO/dichloroethane is shown in Scheme 1), in a ratio of from about 1:10 to 10:1, and is cooled to 0xc2x0 C. under an inert atmosphere, e.g., nitrogen or argon. Following the cooling step, the DAPD is diazotized at the 2-position with an organic nitrite, e.g., tert-butyl nitrite, and halogenated with a metal halide Lewis acid, e.g., antimony trichloride, at room temperature. The reaction produces 2-CdA in high yield. The reaction is unlike any other reactions for diazotization/substitution at the 2 position of a 2-amino purine nucleoside or 2-amino-2xe2x80x2-deoxy purine nucleoside because the diazotization is performed on a unprotected nucleoside. It is the selective combination of solvents in a particular ratio that allows the diazotization to proceed; the diazotization is a key step in this transformation. If only a polar aprotic organic solvent is used in the method, the diazotization reaction does not occur. Similarly, if only a nonpolar aprotic organic solvent is used in the method, the diazotization reaction fails. The chloride transfer, which employs metal halide Lewis acids, such as SbCl3, is very efficient.
As indicated above, the role of the solvent in the halogenation reaction has been found to be critical. A series of TBN/SbCl3 chlorination reactions using a number of aprotic polar organic solvents and non-polar organic solvents with varying solvent ratios were performed. It was determined that the reaction proceeds when the ratio of aprotic polar organic solvent to non-polar organic solvent is between 10:1 and 1:10. The preferred solvent ratio is 1 part aprotic polar organic solvent to 4 parts non-polar organic solvent. The reaction will not proceed when 100% non-polar solvent is used, nor will the reaction proceed when 100% aprotic polar organic solvent is used. Thus, the present inventors have discovered that there is a specific combination of solvents in a particular solvent component ratio range that is required for a successful halogenation reactions.
After the diazotization/substitution reaction is complete the reaction mixture is typically dried, using, e.g., a rotary evaporator, and neutralized. Subsequently, the crude product should immediately be stabilized by chromatography over a DVB (divinylbenzene)-cross-linked polystyrenic resin column, e.g., Amberchrom CG161 (Rohm and Haas, Philadelphia, Pa.). If this product-stabilizing column chromatography step is not performed, and the crude reaction mixture is stored, even at 0xc2x0 C., the product will degrade over a period of about two days. The stabilized product can be further purified by subjecting it to a strong cation exchange resin column chromatography step, e.g., Dowex, (available from many commercial suppliers, such as Sigma Chemical, St. Louis, Mo. or Supelco, Bellefonte, Pa.) and the pure product, e.g., 2-CdA, can then be recrystallized from water.
The Amberchrom CG161 XUS resin column is prepared, typically so that about 4 g of 2-CldA per L of resin is applied. Two-thirds of the resin is removed from the column and slurried with the reaction mixture and then loaded onto the column. The column is washed with water at a flow rate of about 30 to about 80 mL/min until the absorbance at 265 nm drops below about 5 or until the 2-CldA begins to elute off the column and then 3 to 6 L fractions are collected. This is followed with elution with 5% methanol in water, and then 30% methanol in water until the absorbance of the eluate at 265 nm is below 10. All fractions containing greater than 75% 2Cl-dA by peak area using HPLC are collected and concentrated on a rotary evaporator at 45xc2x0 C. The collected fractions are concentrated to a gum, which is at a stable state and can be left for up to 7 days if necessary.
The gum is dissolved in water and then concentrated to a concentration of 12-15 g of 2-CldA/L. This solution is then charged onto a Dowex 1xc3x974 anion exchange resin column. The column is eluted at about 140-240 mL/min, first with water until the absorbance of the eluate at 265 nm is below 10, followed by 10% methanol in water, 15% methanol in water, and finally a 25% methanol in water wash until all of the 2-CldA has eluted off the column. Fractions of about 2-6 L each containing 2-CldA are collected and assayed for purity by HPLC. The fractions that contain  greater than 90% pure 2Cl-dA (by HPLC) is adjusted to pH 7.5 or greater by using 1.0M sodium bicarbonate solution to achieve a concentration 10 mM sodium bicarbonate. These are saved individually, without pooling. A second Dowex 1xc3x974 anion exchange resin column is prepared, with about 1 L of resin per 10 g of 2-CldA. The column is equilibrated in 10 mM sodium bicarbonate solution before the 2-CldA charge is loaded. The charge is made up of the fractions from the previous 1xc3x974 column. The fractions are loaded onto the 1xc3x974 column in the order that they eluted off the first 1xc3x974 column. After the column is loaded, the first eluant, 10 mM sodium bicarbonate in water, is started over the column. Once the majority of the 2-CldA is eluted off the column, the buffer is switched to 10% methanol in a 10 mM sodium bicarbonate solution. The column is washed with this eluant until 90% or more of 2-CldA has eluted off the column. All fractions that contain 2-CldA at greater than 98% purity by HPLC are concentrated in a rotary evaporator at 45xc2x0 C. under vacuum.
The main ( greater than 98% pure) product pool is evaporated to a concentration of about 22 g 2-CldA per liter. The concentrated pool is filtered using a Buchner funnel and Whatman 54 hardened filter paper. The filtered solution is sealed and placed in a refrigerator for 17 hours at about 8 to 14xc2x0 C. for crystallization. The concentrated solution should remain at about 8 to 14xc2x0 C. for at least 14 hours. The crystallized 2-CldA is collected by filtration. The solids are washed with about 50 to 150 mL of cold water, i.e, at from about 5 to 10xc2x0 C. Both the solids and the filtrate are assayed for 2-CldA using HPLC.
The crystallized solids are redissolved in 10 mM sodium bicarbonate solution at approximately 4 to 5 grams of 2-CldA per liter and then concentrated down to about 22 grams per liter using the rotary evaporator. The concentrated solution is then filtered and placed in a refrigerator for about 17 hours, or overnight for recrystallization. After about 17 hours, or overnight, the solids are filtered and both the solids and filtrate are assayed by HPLC.
If there is a significant amount of 2-CldA in the filtrate from the final recrystallization which is greater than 99% purity by HPLC, then the filtrate is concentrated and recrystallized to recover 2-CldA. All the product is 99% or greater pure is placed in a vacuum oven at a temperature of between about 37xc2x0 and 45xc2x0 C. for about 24 hours to dry. After drying the crystals are ground up and dried until the water content is about 2% or less by weight. The crystals are weighed for a final yield.
For maximum recovery, fractions with  less than 98% pure 2-CldA from the second Dowex column are pooled and reprocessed over another 1xc3x974 Dowex column. These clean [ greater than 98%] fractions are combined with the filtrates from previous recrystallizations. This solution is concentrated and recrystallized as described.
The product can be analyzed by any of the common structural analysis methods familiar to those of skill in the art, such as nuclear magnetic resonance (NMR), ultraviolet (UV), or infrared (IR) spectroscopy, or by elemental analysis and optical rotation. The overall yield of 2-CdA from DAPD achievable by the methods of the present invention is approximately ten fold (1000%) greater than obtained by the methods reported in the prior art, e.g., U.S. Pat. No. 5,208,327. Thus, the methods of the present invention are clearly superior in yield and simplicity relative to the methods disclosed by the prior art.
The improved methods of the present invention also permit the synthesis of novel 2-halo-6-aminopurine morpholino compounds. These morpholino compounds are useful in, e.g., synthesizing polymers which can bind specifically to polynucleotides with specific sequences. Thus, they are useful for the detection of specific sequences of polynucleotides, and are potentially useful as inactivators of specific genetic sequences.
The novel 2-halo-6-aminopurine morpholino compounds of the invention have the formula: 
where X is F, Cl, Br, or I and where R1 is aryl, alkyl, aklyoxy or aryloxy. The novel morpholino compounds of the invention can be prepared, e.g., according to Scheme 2, below. 
A 2-amino-6-halopurine nucleoside, prepared according to the methods disclosed above and in the Examples, below, is first N-protected with a carboxylic acid chloride and this intermediate is treated with sodium periodate, which cleaves the ribose sugar ring between the 2xe2x80x2 and 3xe2x80x2 carbons, yielding a dialdehyde. The dialdehyde is reacted with ammonia, which results in a morpholino ring having 2xe2x80x2 and 3xe2x80x2 hydroxyl groups. Sodium cyanoborohydride treatment reduces the ring hydroxyl groups, yielding the novel morpholino compounds of the invention. The synthesis of other morpholinopurines are disclosed, e.g., in U.S. Pat. Nos. 5,185,444 and 5,521,063.
The following non-limiting examples are provided to illustrate the invention. Modifications and variations of the methods and compounds disclosed herein will be apparent to those of ordinary skill in the art, and are intended to be within the scope of the invention.